#include <iostream>
#include <cmath>
using namespace std;

long double area_of_square(long double side=0){
    return side * side;
}
long double area_of_circle(long double radius=0){
    return radius * radius * 3.1415926;
}
long double area_of_triangle(long double s1=0,long double s2=0,long double s3=0){
    double p=(s1+s2+s3)/2;
    return sqrt(p*(p-s1)*(p-s2)*(p-s3));
}
int main(){
    long double a,b,c,d,e;
    cout<<"To calculate the area of a square, please input the length of one side:";
    cin>>a;
    cout<<"area_of_square("<<a<<"): "<<area_of_square(a)<<endl;
    cout<<"To calculate the area of a circle, please input the length of the radio:";
    cin>>b;
    cout<<"area_of_square("<<b<<"): "<<area_of_circle(b)<<endl;
    cout<<"To calculate the area of a triangle, please input the lengthes of three sides (separated with space):";
    cin>>c>>d>>e;
    cout<<"area_of_triangle("<<c<<","<<d<<","<<e<<"): "<<area_of_triangle(c,d,e)<<endl;
}
